Television system



Oct. 12, 1937. v J. w. LEGG 2,095,39l

TELEVISION SYSTEM Filed April ll, 1927 3 SheefSwSheet 1 WITNESSES; IINVENTOR 5. MW Jase/oh VV. Legg Oct. 12, 1937. J. w. LEGG 2,095,391

v TELEvIsIoN SYSTEM Filed April 11, 1927 s sneets-shet 2 fig-3-hillll'l'lllll WHNESSES; lNvEwToR f MWM Jose/oh l/1/. Legg Oct. 12,1937. J. w. LEGG 2,095,391

TELEVIS I ON SYSTEM Filed April ll, 1927 5 Sheets-Sheet 3 ved 804 80gob/ MWWNWWWMWWWWWMWWM C MM A Zero Amp//fude i Max/Mum /lmp//V-UdeWITNESSES; iNvENToR 5. MWM Jose/oh Legg '/I L I 30 defined point oflight.4

Patented Oct. 12, 1937 Parent ormer aosasei i TELEvrsroN SYSTEM JosephW. Legg, Wilkinsburg, Ita., 'assgnor tom Westinghouse Electric&'Mannfactnring Company, a corporation of Pennsylvania Application April11, Miseria! Ne. 182,651:

' as claims. (ol. its-6).

i `This invention relates to systems for the transmission of views bycommunication systems, such asradio`.' "It is an object o'f thisinvention to produce i synchronism between .the scanningvand-reproducing. `devices without requiring an additional communicationchannel for this purpose,

Itisa further object of this invention to combinea synchronizing meanswith the view to be transrnitted. i i I i 'It is a further 'object ofthis invention to send over the communication channel a characteristic4impuls'e at corre'sponding phases Of eachitraverse ofV the view by thescanning device and to automatically position the reproducing device inaccordance with said phases of the traverse by V means ofsaird'impulses..

`It is a further object of this invention to produce`` an Optical systemin which the Only parts required to move rapidly shall be the mirrorsys'- tem of an oscillograph.

It is a further object of this invention to provide a light source theintensity of which may be rapidly vari'ed in accordance with theillumination of successive points in the view to be Htransmitted.

` It is a further object of my invention to provide ahlinear lightsource which, by means of a cylindrical lens, may be made to give7 awell- It isl a further object of my invention to provide avariablesource of light in which the brilliancy shall be controlled by animpressed potential. i

`,It` is a'further object ofrmy invention to pro- .duce a conductivecolumn of vapor to47 emit light and'tocontrol the brilliancy thereof byvarying the potential along it. i

` Itisa further object of invention to com- 44) bine a linear source oflightl With an Optical system,l;including a moving part, in such amanner Y that successive portions of said sourcemay be brought, inturn,`` into operative relation to the Optical system. .5 Other objectsOf my invention' will be apparent from the following detaileddescription and the accompanying drawin'gs'in which,

Figure 1 is a diagram, partly in perspective, illustrating the scanningapparatus, to Fig. 2 is a diagram illustrating the movable mounting ofthe lenses shown in Fig. 1,

Fig.'3 is a diagram, partly in section, illustrating the. receivingapparatus,

* Fig. 4 is a diagram, in perspective, illustrating o.) the 7opticalparts ofv the receiving apparatus,

Fig. 5 is a diagram to assist in the explanation Y of the Operation ofthe vtransn'litting system,

. Fig. 6 is. an illustration of a modifioation of the optical system ineither the receiving apparatus or the scanning apparatus, and 5 Fig. 'Zis a diagramillustrating a means Vfor producing a slow movement of oneof the Optical parts shown in Fig. 6.

As shown in Fig. 1, an object Or a view l is visible through a window 2.Although the draw- 10 ings are intended to Suggest that the view I is'out of doorsand the Optical apparatus in a house, it will be obviousthat a small boxmay enclose' the Optical parts and the window 2 willthen. be an Opening in one wall of the box; i 15 At one side of thewindow, the wall is opaque and dark, as indicated at 3. `At the oppositeside of the window a portion of thewall is brightly illuminated, asindicated at 4. The illumination may, for example, be accomplished bylamps 5 f and, if desired, the surface of the wall flush with 20 thewindow and with'the dark surface 3m.ay be covered with ground glass orOther means for rendering the bril'liancy uniform thereover. i i xThescene to be'soanned by the Optical system Vin Fig;v 1 includesthe brightsurface 4 and the 5 dark surface 3, as'well as the view or objectsbeyond the Window 2.

On the side of the window opposite the object or view I, a plurality oflenses 6 are positioned, Preferably, these lenses are, as shown in Fig.2, numerous and comprise a large circle of lenses, whereby first onelens and then another may be brought into position inn front' of thewindow without requiring a high rate of Vspeed for the movement of thelenses. In the specific form of mounting, indicated in Fig. 2, thelenses are secured in a disk 'l Which is driven by an electricl motor 8.suitable reduction gearing may be employed togive the proper speed tothe Wheel 'l and suitable openingsin the disc 'i provide for the passageof `light through the lenses S.

On Fig. 1, the direction of movement of the lenses 6 is indicated by anare having a center I ll which, in actual construction, would be the 4center of the Wheel 1. For the sake of clearness, the Wheel is not shownin Fig. 1.

The lenses' 6 are cylindrical, their geometric axes beingl arrangedradially'of the disc 'IV andV their Optical axes being perpendicular tosaid disc. For the short distance that any One lens 6 moves while inoperative relation to the rest of the Optical system, the motion may beregarded as pure translation at right angles to both axes. I'helens 6 isbetween the window 2 and a mirror II which is mounted on a device thatcauses the mirror to oscillate rapidly.

Any suitable means for producing rapid oscillation may be employed. Iprefer to support the mirror upon the movable conductors I2 of anoscillograph and to send a high-frequency current, produced in anyfamiliar or suitable manner, through the oscillograph to oscillate themirror. When the oscillations are produced in this way, it is preferablethat the natural period of the Vibrating system shall be the same asthat of the current supplied. Between the mirror I I and the lenses 6, alens I3 is provided.

The ribbon of light which arrives at the mirror I I from the. lenses 5from a point on view I is refiected, passing a second time through thelens I3, and reaches a photo-cell I4. A shield I5, having a smallVertical Opening I6, is provided in front of the photo-cell I4 in orderto give definiteness to the point in the scene I corresponding to theinstantaneous position of the optical system.

The lens I3 focuses the light from the mirror II and lens 6 upon thewindow I6. The quantity of light entering the photo-cell is, therefore,that from a larger area in the view I than the size of the opening I6would command if unaffected by the lens. If desired, additionalconcentration may be afforded by another lens between window IG andphoto-cell I4.

The light from the scene passes through the lenses 6 and l3 and isreflected by the mirror II. Only the light from a definite point in thescene will, however, pass through the window I 6. Light from otherpoints will be stopped by the screen I5. Thus, at each moment, adefinite point in the scene is correlated to the window IS. This pointchanges from moment to moment, one coordinate thereof being dependent onthe motion of the mirror I I and another upon the motion of the lenses6.

The photo-cell I4 is connected to any well known or desired form oftransmitting system whereby the radiations sent out by the transmittershall be modulated in accordance with the illumination of the photo-cellI4, the amplitude of the radiation corresponding at each moment to theillumination of the cell.

A conventional radio transmitting system is illustrated in the drawingsfor the purpose of showing how the photo-cell l4 may control theamplitude of the radiations. The actual structure of the Vacuum-tubecircuits is not a feature of my invention. In the circuits illustrated,the photocell M controls, in the usual way, a modulator tube I1 whichacts to divert more or less energy from the oscillator tube I8. Theoscillations from the tube IB are radiated by the antenna IS.

In Fig. 3, the receiving antenna 2I is tuned to the frequency of theoscillations generated by the tube IB at the transmitter. A detector 22is connected, in any usual or desired way, to the antenna 2I. The outputcircuit of the detector includes a plate battery 23 and a resistor 24.Preferably, a second battery 25 is inserted between the resistor 24 andthe filament of the detector 22. A condenser so small that it is oflarge impedance to all except the very high frequency, may, if desired,be connected across the output of the detector to ensure that the highfrequency components of the plate current shall not affect theapparatus. Between the battery 23 and the resistoi` 24, a condenser 26is provided in parallel with an inductor 21. The inductor 21 is also theprimary of a transformer, of which 28 is the secondary. The condenser 26and the inductor 21 together constitute a network interposed in thecircuit from the plate to the filament of the tube 22. The frequency, towhich the network or parallel-resonant circuit is tuned, is thefrequency of the movement of the mirror II in Fig. 1.

One terminal of the secondary 28 is connected to the grid of a tube 29,and a battery 3Il is connected between the other terminal of thesecondary 28 and the filament of the tube 29.

The plate current of the tube 29 is supplied from a battery 3l. Ifdesired, the battery 25 may be replaced by a portion of the battery 3I.This can be done by connecting the left-hand terminal of resistor 24 toan intermediate point of battery I. The plate circuit includes theprimary 32 of a transformer, the secondary 33 of which ls connected tothe moving conductors 34 of an oscillograph 35. The moving conductors 34carry a mirror 35. If desired, a condenser may be shunted across theprimary 32 for tuning, and an additional inductance, for further controlof the tuning, may be inserted in series with the primary 32. A tuningcondenser large enough to compensate for the inductance 33, and also forthe inductance. of the receiving device 34 may, if desired, be includedin the secondary circuit.

The battery 3! serves to supply also the plate circuit of a tube 31. Byproperly proportioning the potential of the battery 23 to that of thebattery 25, the average potential of the grid of the tube 31 isdetermined. The potential also depends on the drop across the resistor24 and the effect of the network 26-21.

The plate circuit of the tube 31 includes a resistor 4; which, ifdesired, may be a heating coil for maintaining the mercury in the tube42 at a temperature near its boiling point. A battery 43, in series witha resistor 44, is connected to the mercury by means of cups 45 and 46which are parts of the lamp 42. The resistor 44 may also serve as aheating coil to maintain the capillarv column 41 of the lamp in avaporized condition. The two terminals of the resistor 4I are connectedto sealed-in electrodes 48 and 49 near each end of the capillary portionof the lamp.

Although I have illustrated a mercury tube having open ends, other formsof mercury lamp may be used, such as mercury-are tubes having a lowpressure of mercury vapor. The portion of the capillary tube 41 betweenthe electrodes 48 and 49: will not generally have liquid therein, butwill be filled with the glowing vapor. It is not essential that, evenwhen the lamp is cold, f

the capillary be filled with liquid. The lamp may be started by acurrent through the ordnary mercury vapor if preferred.

The optical portion of the receiving system includes mirror 36, a lens50 for bringing to a focus adjacent the lens 5I, the light from the lamp53 which is reflected by the mirror 36. The optical system also includesa plurality of lenses 5I mounted in a disc. The optical system is bestillustrated in Fig. 4, wherein the screen 52 receives light from thelamp 53 through said optical system. The screen 52 may be a photographicplate for recording the transmitted view or it may be a ground glass ora projection screen or an imaginary plane on which is focused an eyepiece, or ocular to be observed by the eye, or through an ocular.

In Fig. 4, for clearness, the several directions are taken perpendicularto one another, but the invention may be used with oblique directions.

The lamp- 53 is shown as'horizontal and extending away from` the readerand toward Vthe right.

l'l'he axisof movement of the mirror 36 is shown parallel/to, and belowand; 'to the' right of, the lamp. For further simplicity of description,it wilil-`l be assumed that the 'center of the mirror is in the planeperpendi'cular toithe lamp at its center, although this'feature is notlessential to,

i near said plane may 'be'regardedi as. parallel tovpotential-responsive device.

the length of' the lamp and tosthe. other: pairflof edges of` the`screen.. The `refiected light is brought, by the lens -lf, to a. focus:upon the: under side of the screen 52.

In Fig. 61, a modification of the optical Vsystem is shown, two mirrorsbeing employed'instead of a mirror and a plurality of lenses. The mirror3% is intended' to be oscifllated atr high frequency by the conductors34, as alreadyexplained.. The mirror tilv is intended to osciliateat alower fre,- quency, the oscill'atiohs of the mirror BI being produced bythe means illustrated in. Fig- '7. Two lensesi 62 and 63 are Vprovidedfor focusing the light upon the screen. The mirror 36' is mounted .uponthe conductors. of the. oscillograph; 3:51. 'The mirror 61 is mountedupon the conductors 64 which, inf this mOdifiGation, are a portion ofthe same os'cill'ograph. In Fig. '1, the

conductors 64' andfthe mirror 6 Il are shown below the conductors 34and; the mirror 35; It will be evi'dent that the position`` may be,lreversed if desired and that it is not necessary to: havethe mirrorshorisontal.,v

In Fig' '7, a synchronous motor 66 isflsh'own which is' intended to bedriven by the same power system as thelmotor 8 in Fig' 2'. Correspondingfrequencies: in the mo-vement. of. the. Wheel I and the rotor` of themotor 65 are thus obtained'.: The

conductors '5.4 have; a high resistance .1.51 in'series with. them,'whereby the mirror'l is essentially'a A battery 'II,` feedingaci-rcularl potentiometer 1'2, Supplies the po- 4 tential'for theconductcrs 613m The moving member '13 of the potentiometer7 is connectedto. one terminal of the. co-nductors; 64 and is driven by the rotor ofthe motor GIS;` I I v In theoperation-of the device, the movement of themirror IfIv in Fig. 1 causes'the window Ha' of the photo-sensitiveinstrumentxto be associated in succession` with a' line-ofpointsextending. horizontally. across the view. The' movement' of thelens' causesf the Window IG' to beflass'ociatedxin succession withpontsatr different heights in the window 2:

The movernentA of the mirror Iflv is much more rapid than that of thelens 6. During any one swing of the mirrorl II, first'one end, thenanintermediate portion;` and then theother end of the lens` i;` isoperatively J related to the mirror Ili and the window- HS. VOnlryajsmaljl portion of:

' the whole lens Eifis operative at any one' instant.

This portion is of small enough axial.` length1to: cause the differencebetween it and a spherical i lens to be without substantial effect; Theillumination of the window IS by .the light from the spot in the scenecorrespondingto the instantaneous position, of the Optical system issubstantially the same as it would be if the7 portioneof lens 6corresponding to the position of the mirror 'II. at that moment werespherical instead' of with the. brightly lighted left-hand. margin of ithe scene, the mirror is moving slowly. Again, at the right-hand end ofits, swing, when lt is associatng; some. point? in: the darkr surface..3 with the window IG, the mirror is moving. slowly., The rate of changein the mirror's motion is greatest at the points in. the swing where itis moving slowly; Overthemid-portionsiof the Swing, the mirror islmoving nearly, although. not

absolutely, at a uniform velocity. Consequently, there will be, in thereproduction, but little distortiorr of theV illumination resulting'from the fact 7that the mirror II 'sweeps more rapidly over some partsof the view I than over other parts. In the extreme positions of f themirror I I, either the brightly illuminated space II or the dark spacea3is associated with the. Window IG. Since each of these two spaces is ofextreme and comparatively uniform illumination, the change in. rate ofmovement: of the mirror in these parts of the swing is unimportant.

As the mirrowV I I swings,v the illumination; of the cell M is; atVfirst veryfgreat, then varies in accordance with thel illuminationof theseveral pointsl of the view and finally becomes zero. Both the zeroillumination and the very great illumination differ greatly from theillumination of any point in the view I seen through the window 2. Thus,atthe extreme left-hand position.` and at` the extreme. right-handposition of the mirror II, the cell' I4 is subjected toa very different`degree of' illumination from that'dur-v ing therest of the traverse.When the mirror II is in such position, that 'the window IIis opticallyassociated with a point inthe dark surface 3, the photo-electric cellI4- tion of the mirror VII is such that light from a spot in theilluminated area 4 reaches the photocell IA, the cell is highlyilluminated, and, 'therefore;` sufiiciently conductiveto cause -thepotential'fof the grid of the tube I'I 7 to beV more nearly positive.Czonsequently, a considerable;

amount 'of'ene'rgy is diverted from the Vacuum?- tube P8, and theoscillations either ceaselentirelyor become very small. Practcallynno ienergy is radiatedby the antenna I9. under these circumstances. i

fIn any other position'of the mirrorv II, the illumination of. thephoto-cell Ill' corresponds to 7the brilliance of some point in the viewI.. Consequently, thephoto-cell I4 is illuminated toan intermediatedegree. Some energy is, therefore, diverted from the tube I8 but notsufiicientto cause the amplitude of the radiations to become zero.

Preferably, the constants of the apparatus are so chosen that the changein the conductivity of the photo-cell I 4 will occur on thestraight-line part of the characteristic curve of this cell. Likewise,the changes in the current, through the tube I1 and in the amplitude ofthe radiations, preferably have a straight-line relation to the changesin the illumination of the cell I4 as the mirror sweeps over the portionof the scene constituting the View I. The darkness of. the surface 3 andthe brightness of the surface 4 are intended to greatly exceed thechanges in the view, whereby the. changes in the amplitude of theradiation at each end of the swing of the mirror I I greatly exceed thechanges during the middle portion of said swing.

It is permssible for these extremes to extend beyond the straight-linepart of the characteristic, but no advantage results from having themextend very far beyond it.

Fig. 5 is a'n attempt to indicate the changes in amplitude of theradiations with changing positions of the optical system. The left-handportion 8I of Fig. 5 corresponds to the brightly illuminated surface Theright-hand portion 83 corresponds to the dark surface 3, and the middleportion 82 corresponds to the window 2.

The combined action of the mirror I I and the lens G'will cause thepoint in the scene optically associated with the Opening IG to explorethe scene by a path which crosses the scene rapidly from side to side,entering the illuminated surface 4 at one side and the dark surface 3 atthe other side. The curve 88 in Fig. 5 is intended to illustrate how thepoint corresponding to the window IB moves, and the accompanying changesin radiation. The serpentine character of the curve, causing it toextend across the figure many times between the right and left edges andonly once between the top and bottom edges, corresponds to the progressof the point.

The sinuosities of the curve are intended to represent the oscillationsconstituting the radiation. It will be recognized that the wave lengthof these oscillations is very much shorter than illustrated by Fig. 5. Adrawing to' scale would show these oscillations of, so short a wavelength that they could not be recognized.

The distance which these sinuosities extend away from the mean positionof the serpentine curve corresponds to the amplitude of theoscillations.

In the portion 8I of Fig. 5, the curve has no sinuosities. This isillustrated at 800,. In the portion 82 of Fig. 5, the ourve hassinuosities of changing amplitude. This is illustrated at 8019. In theportion 83, the amplitude'is a maximum, as illustrated at 800.

Throughout the region 8I and the region 83, the rate of movement of themirror I I is changing rapidly, but, since the brightness of the surface3 is always zero and that of the surface 4 is uniform, the amplitude isuniform (and minimum) in the region 8I and also uniform (and maximum) inthe region 83. The change in rapidity of movement of the mirror II is,therefore, without effect upon the outgoing radiations. Over the region82, the rate of movement of the mirror II changes only slowly. Verylittle distortion will, therefore, be produced by the circumstance thatthe mirror passes more quickly over certain portions of the scene thanover other portions.

The radiations are received upon the antenna 2I, represented in Fig. 3,which is so tuned that other frequencies are of little effect upon thegrid circuit of the tube 22 which acts to detect the signals.

The plate current of the detector 22 will vary in accordance with theamplitude of the radiations. Consequently, the plate current will varyirregularly while radiations corresponding to the region 82 in Fig. 5are being received, and will show a large and abrupt change when theexploring point enters the region 3, and a large and abrupt change inthe opposite direction when the window I6 is correlated to a point inthe region 4.

The tuned circuit 26-21 is thus subjected, at the instants of each endof the traverse, to impulses due to the sudden change in the characterof the plate current. The impulses are of one character when the mirrorII is at one end of its swing and of the opposite character when it isat the opposite end of its swing. They, therefore, set the circuit 26-21into oscillation at its natural period. This period is adjusted tocorrespond to the period at which the mirror II is oscillated. Theimpulses caused by the bright surface 4 and the dark surface 3 thusinsure that the phase of the current circulating in the network 26-21will always agree with the phase of the movement of the mirror II.

The tube 29- delivers to the primary 32 a current which is controlled bythe secondary 28, and which, therefore, agrees in phase with themovements of the mirror I I. To add still greater certainty to thesynchronizing effect, the plate circuit of tube 29 may be tuned by acondenser in parallel with the primary 32. Preferably, the lnductance inthe tuned circuit is not all included in the primary, but a portion, inseries with the primary, is added for Convenience in adjusting thetuning.

The secondary 33 is energized from the primary 32 to deliver current toconductors 34, which causes the mirror 36 in the oscillograph 35 tomove. The provisions just described for insuring the synchronism causethe movements of the f mirror 38 to agree accurately with those of themirror II. The position of a selected point in the view I correspondsaccurately, so far as its right and left co-ordinate is concerned, withthe position of the corresponding point of screen 58 determined by themirror 36.

The Vertical coordinate of the point in the view I optically associatedwith the photo-cell I4 depends upon the position of the lens 6. Thisposition ls changed by the rotation of the disc 1, which, being drivenby the motor 8, may be made very regular, depending only upon thefrequency of a Commercial power supply. Similarly, the movement of thelens 5I in the receiving apparatus shown in Fig. 4 may be produced by amotor similar to the motor 8 and fed from the same power supply. Thecenter of the wheel or disc carrying the lenses 5I is indicated at 15 inFig. 4.

The movement of the lenses is slow, as compared with the movements ofthe mirrors |2 and 36. It is, therefore, feasible for an operator toadjust the position of one set of lenses 6 or 5I relative to theotherjif the appearance of the reproduced picture shows that such anadjustment is needed.

The light for the receiving apparatus is supplied from a linear lightsource 53. In one extreme position of the mirror` 36, light from thissource is refiected to a point near one end off a lens SI. As themirror,36 swings,l the light is directed to successive lportons of Vthelens:I until, at the other end, of the Swing, it is` refiected to apoint near the other end of said lens.` Y -11 1 As the lens 5I passesacross the screen 52, successive portions of the linear light source53;are concentrated toa point onithe screen 52..

When the lens 5I passes, out of operative position and.- the-next lens5I enters operativeposition, the illuminated point on the screen 58changes abruptly from one sidefof the screenVV .to thejother. -f i 7`ThemovementV of the mirror 36 causes the spot of light to travellengthwiseof the screen 52;

rthat,.is,V between the two edges shown in Fig. 4 asshort edges.4Themovement of'the lenses 5I i causes the illuminated 7point to travel.between the edges shown .as longf'edgesin said figure.

The movement of .the illuminatedpointfin re-`` sponse, to the motion of;the mirror 36, is (prefer-i ably greater than the l'ength of the screen52. Consequently, the bright surface 4 and the dark surface 3Y are: not,represented 'upon the screen 52.

The changes in the intensity Vof the lightflreceived from the several.pointsthroughout the. 'V

scene I, 33.; and 4, Fig. 1, cause. changes in the magnitude of thecurrent in the 'plate circuit of thetube 22,.iFig. 3. The potential dropacross the; resistor 24 .isjthereby varied, with the result thatvariations occur in the plate circuit of the tubeir'i'lfandcausencorresponding variations i in*` the` potenti'a'l'fdrfopl acrossthe resistor My' 'The potential7 acrossfthexresi'stor 4I isimpreSSed'between. the electrodes 48 and 49; Thisis added to the;- potentialacross this portion of the arc in thefmercuryt vapor orother-vaporalready established by .the source 43 andy controlled by thestabilizing'resistor 44.

If 'the changes in radiation andvin thev``4 plate circuit,l from. thetube 22: are in such 7direction thatv theapotential difference acrossthe resistor 4I increases for brightv portions offthei picture,

thjebattery 43 will be arranged to give a poten- `tial* along thecapillary-itube in the same direction as the potential. across theresistor 4I, but, if-.thewchanges in the potential acrossv theVresistorr4=I arein` the opposite direction. to'the changes imillumination of. cell Iz4', the battery '43' will be .connected -in= theopposite direction. Consequentlmwhether. the .electrodes 48 andIIIladdtoV the' potential across the portion of the capillary betweenthemnorldiminishc it; the result, in either case; is that theinstantaneousfpotential across? this part ofpthe `capillary `isV greaterwhen the point `in the scene I' which, at the moment;l is

correlated` to the window Hi; is lbrighter. The

potential along. the capillary determines the brightness of` the lightemitted by the vapor therein. Consequently, the light source is morebrilliant when the corresponding point in the scene I is bright. i i

Another way of enablingfthe changes in illumination om. the screen52lt'o .certainly be always :inithelsame direction astthe changes in thescene isV teureplace the grid: leak and condenser at' the tube 22 in:Fig; 3: by an adjustable C battery. The tube` can then be adjusted toeither the lower curved part or' the upper curved part of the;characteristic.. VThis will cause'7 the sense of thetchanges: in the..output current tox depend upon the adjustment.. i

`.Themovernent' of, the mirror Bli-and of l.the lenses 5I alwaysassociate some portion of. the

.lightsource 53-.withV apoint in 7thescreen 52 corthan the mirror I I orthe mirror (iii.

by a rotating potentiometer.

responding to that point in the scene I deter-' i mined b-y the positionof the mirror II and the lenses 6. Since the mirrors II and' 36 alwaysmove in. synchronism, and theV lenses 6 and 5I always move atthe same'speed and are readily adjusted to synchronism, the illuminated point onthe screen 52 always corresponds to the point in the scene I opticallyassociated at that moment with the window IG. reproduction of the scenescreen 58.

Ther speed of .thelenses 6 and 5I is so chosen that the Verticalco-ordinates of the corresponding points on the Screen and'in the sceneare varied throughout their amplitude rapidly enough to Vcausepersistence of vision to make the picture on the screen 52 appear torepresent the actual movements of the moving' objects-in Vthe'view I. r

The rate of movement ofthe mirrors II and 36 is great enough Vto causethe horizontal co- Vordinate of the corresponding points to vary`Vthroughout their amplitude many times during one cycle of the variationof the Vertical coor-` dnate; as many times as there should be lines inthe picture to give a satis'factory "grain".

Thus, if the picture isto have 60 lines to the inch, the` mirror I Imust make complete vibrations for each movement of the 7lens 6 over oneinch, and the'lens ti must move at such a speed that the. completeVertical height of the picture is traversed byxfit in at least a tenthof a second.. 7In the `Operation of7 the Optical system illustrated inFigs. 6 and 7, the moving lenses 5I are replaced by a mirror whichmovesmore slowly The movement of the slowly moving mirror is'controlledThe arm of this potentiometer, being drven'by a synchronous motor, movesat a Constant speed. Motors for driving the potentiometer arms maybeused at rboth the sending and -the receiving station, or a wheelcarrying lenses may be used at one station and af potentiometer atanother. In either case, equality of speed is insured by Connecting themotor to a common power supply. I

As the arm 13 traversesthe potentiometer 12, the Vpotential impressedupon the oscillograph conductors 54 gradually increases, causing themirror GI to swing farther and farther. As the arm 13 passesV from oneend of the potentiometerv 12 to the other across the adjacent ends ofthe resistor, the potentialv impressed upon the conductors 64changesabruptly. The movement of the mirror GI, therefore, will closelysimulate The resultI is'that a` I is obtained upon the the action of thelenses, comprising'a gradual to be scanned for i'mpressing on thescanning device an intensity effect differing from that of substantiallyany found in said subject, means controlled by said differing-intensityproducing means, for producing a characteristic impulse at each traverseof said subject by the scanning device and oscillatory means controlledby said impulses for producing a corresponding position of thereproducing device.

2. In a television system, a sending instrument including means fordelivering carrier energy, a scanning device adapted to make traversesof a subject to be scanned and means adjoining said subject forproducing a characteristic modulation of said carrier energy duringportions of each traverse by the scanner where subject elements areabsent and a receiving instrument including an oscillatory memberadapted to move in accordance to said modulation, whereby the traversesin the receiving instrument will be maintained in fixed relation tothose in the scanning device.

3. In a television system, a sending instrument including means fordelivering carrier energy, a scanning device adapted to make traversesof a subject to be scanned and means for modulating the carrier energyin accordance with the intensity of the elemental areas of said subjectcovered by the scanning device during said traverses, means forpresenting to said scanning device at the extremity of each traverse anintensity differing from that of substantially all the elemental areasin said subject, whereby a corresponding difference in the modulation isproduced and a receiving instrument including an oscillatory memberresponsive to said different modulation..

4. In a television system, a sending instrument including means fordelivering carrier energy, a scanning device adapted to make traversesof a subject to be scanned and means for modulating the carrier energyin accordance With the intensity of the elemental areas of said subjectmet by the scanning device during said traverses, means for impressingupon the scanning device between traverses of said subject an intensitydiffering from that of any of the elemental areas in the subjectywherebya corresponding difference in the modulation is produced and a receivinginstrum ent including an oscillatory member responsive to said differentmodulation and means for preventing response of said member to themodulation corresponding to brightness of the scene.

5. In a picture reproducing device, a linear source of light, a screenand means for projecting the light from successive portions of saidsource upon the screen, said portions being in a line corresponding tochange of one coordinate in the picture to be reproduced and means fordeflecting the light in a direction at an angle to said line.

6. In a picture reproducing device, a linear source of light, acylindrical focusing device, means for directing the light fromsuccessive portions of said source progressively upon successiveportions of said focusing device and means for moving said focusingdevice at an angle to its length.

7. In a television system, a scanning device, means for producingradiation comprising a carrier Wave mcdulated in accordance with theintensity of the elemental areas of a subject selected by the scanningdevice, means independent of said subject and scanned by said scanningdevice for producing a characteristic modulation of said carrier Waveupon each traverse by said scanning device, a reproducing deviceincluding means for producing a scanning medium of an intensitycorresponding to said elemental area modulation and means controlled bysaid characteristic modulation for directing said scanning medium inaccordance with the movement of the scanning medium at the transmittingend.

8. In an optical system for view-transmission,v

a lens having a cylindrical surface, means for moving said lens at anangle to the axis of said surface, Whereby successive positions of saidaxis lie in a plane, a mirror and means for oscillating said mirrorabout an axis forming an angle with the normal to said plane.

9. In an Optical system for view-transmission, a lens having acylindrical surface, means for moving said lens at an angle to the axisof said surface, whereby successive positions-of said axis lie in aplane, a mirror and means for oscillating said mirror about an axisparallel to said plane.

10. In an Optical system for transmission of views, a plurality ofcylindrical lenses, a carrier therefor, means for moving the carrier tobring` said lenses successively into the same position, a mirror, andmeans for causing said mirror to oscillate about an axis substantiallyparallel to the plane of rotation of said lenses.

11. In an Optical system for transmission of views, a plurality ofcylindrical lenses, a carrier therefor, the lenses being mounted thereonin a circle with their several axes radial thereof, means for rotatingthe carrier about the center Of said circle, a mirror, and means forcausing said mirror to oscillate about an axis substantially parallel tothe plane of rotation of f said lenses.

12. In .an optical system for transmission of views, a plurality ofcylindrical lenses, a carrier therefor, the lenses being mounted thereonin a circle with their several axes radial thereof, means for rotatingthe carrier about the center of said circle and a mirror mounted tooscillate in such direction that it will sweep lengthwise over one ofsaid lenses.

13. In a picture-reproducing system, a linear source of light, a screen,a vibratory mirror, a plurality of cylindrical lenses and means forcausing said lenses to successively pass intermediate' said vibratorymirror and said screen, whereby the light from successive portions ofsaid source is caused to fall upon said screen.

14. In a view-transmission system, means for transversely scanning asubject, means adjacent to said subject cooperating With said scanningmeans for the production of periodic electrical impulses representativeof the rate of scanning, oscillatory scanning means at a receivingstation, and means whereby said oscillatory scanning means isconstrained to vibrate in synchronism` with said periodic electricalimpulses.

15. In a television system, a transmitter comprising scanning meansincluding a ray of energy, a reproducing device comprising similarscanning means, means exclusive of a subject to be scanned and disposedwithin the range of Operation of said ray for producing, in combinationWith the scanning means, a characteristic impulse at a denite frequencyin the energy output of said transmitter and means for utilizing saidcharacteristic impulses for producing corresponding momentary positionsof the scanning means of said reproducing device.

16. In a system of the television type, means for scanning a subject,means adjacent to said subject and adapted to be scanned by saidscanning means throughout the scanning period for the production of acontinuous train of periodic electrical impulses representative of therate of scanning.

17. In a system of the television type, means aooasci;

the energy output of said systemnmay be-pro`-;

duced for synchroni'zing purposes.

18. In a system for the transmission trical impulses to producepictures, an area of varying light reactivevalue arranged in effectiveposition to bescannediwith the object to be pictured, and means forscanning said area coordinately with said object, for producingelectrical impulses of scanning frequency. I

19. In a system for the transmission of elec- 'trical impulses toproduce pictures, an area arrangeol in effective position to be scannedwith the object to be pictured, andmeans for scanning said areacoordinately withV said object for producing electrical impulses ofscanning fre'- quency, the elementary units of said area having a lightreactive value whichV is a function of their position in said area.

20. In a system for the transmission of electrical impulses to producepictures, an area arranged in effective position to be scanned with theobject to be pictured, and means for scanning said area coordinatelywith said object for producing electrical impulses of scanningfrequency, the elementary units of said area having a light reactiveValue which is a function of the effective position of said area withrespect to said object.v Y 21. Ina system for the transmission ofelectrical impulses toproduce pictures, an area arranged in effectiveposition to be scanned with the-object to be pictured, and means forscanning said area coordinately with said object for producingelectrical impulses ofv scanning 'freduency, said area 'having a lightreactive value varying in accordance with a system 'different from thepicture. i

22. In a system for the transmission of electrical impulses to producepictures, a shaded border arranged to be effective as if bounding theobject to be pictured, and means for scanning said border coordinatelywith said object for producing electrical impulses of scanningfrequency.

23. The step in the method of synchronizing a transmitter and receiverof electric impulses for the production of pictures which comprisesscanning an area of varying light reactive Vva-lue co-V and a receiverofelectrical impulses for the pro- Y duction of pictures which comprisesbounding the object to be pictured with a shaded border, producing acurrent corresponding to the illumination from successive elementaryunits of said object and border, and utilizing the current correspondingto said border to control the frequency i of a receiving scanningsystem.

26. In a system for the transmission of electrical impulses to producepictures, a shaded border arrangedas if bounding the object to betransmitted, means-for scanning said object and said border toproduce acurrent varying with the illumination from successive elementary unitsof said object and border, means for transmitting eler;

Vimpulses alternately of picture and scanning frequencies, .means for'detecting a low. frequency component of 'the transmittedfimpulses,meansf for filtering out substantially all but the fundamental frequencyof said Component, and means for utilizing said fundamental frequency toactuate a receiving scanning means.

' '28. In asystem of the television type, a subject to `rbe scanned, ascanning ray, means for Vcausing said ray to scan said subject forcausing energy to be modulated according to the light 'intensity of theelemental areas of said subject,

and means disposed beyond the boundaries of said sub-ject but withintheioperating range of said scanning ray for impressing upon said energya pieriodic characteristic impulse for synchronizing purposes.

29. In apparatus of the television type, a subject tobe scanned, ascanning ray, means; for causing said ray to sweep= across said subjectand beyond at least one of its edges and means disposed beyond the areaof said subject but within the operating range of said ray for producinga periodic characteristic impulse in the output energy of saidapparatus.

30. A television synchronizing system including a photoelectric cell,screening means of varying optical density for optically modulating thesame so as: to produce a sinusoidal electric'wave form, alternately withthe signals produced by scanning each line of the picture, means fortransmitting this wave form, means for receiving this wave form,rmeansfor separating it from other wave forms due to signals present on thesame transmission channels, and rmeans for applying it to eifect thesynchronization of said television system;

31. In television transmitting app-aratus electro-Optical apparatusmeans for the production o-f synchronizing signals, between groups ofpicture signals, each of said vgroups representing a single linescanning, including screening members whose degree of opacityrvariesaccording to a sinusoidal law, in respect to distances measurable uponsaid screening members, cooperating with the vbalance of thetransmitting system to cause the said synchronizing signals to Vbe of asinusoidal form.

32. A television transmitter including op-tical reactive means effectivebetween thescanning of each line and that of the line next scanned, saidmeans o-ptically producing synchronizing signals `of a predeterminedrate of amplitude change and of a predetermined range of amplitudeValues, an image to be scanned having a range of light Values at leastas great as has said Optical reactive means, piortions o-f said imagewhich have said light Values being so positionedl relative to oneanother as to produce image signals at least Vsome of which have a rateof amplitude change greater than` Vthat of said synchronizing signalsand the amplitude range of which isnever greater than the amplituderange of said synchronizing signals, and means for alternatelytransmitting said image signals and said synchronizing signals wherebysaid synchronizing signalsV may be effectively separated and selectedfrom said image signals and from extraneous signals at a televisionreceiver.

33. Means for transmittng television and synchronzing signalseifectively separable from one another including Optical means forscanning in turn each line of an image, means optically discrete fromsaid scanning means for modifying the light falling upon said Opticalscanning means after the scanning of each line, said modifying meansbeing provided with a substantially continuous gradation froms'uostant'ially maximum light' reactive value to substantially minimumlight reactive value, and means for alternately transmitting said imagesignals and said synchronizing signals Whereby said synchronizingsignals may be efiectively tuned and distinguished from extraneoussignals at a television receiver.

JOSEPH W. LEGG.

